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Asked if he would be leaving self-isolation on Friday, the spokesman said: “We’re following the guidelines from Public Health England (PHE) and from the chief medical officer which state that you need to self-isolate for a period of seven days, so no change in that.”

Number 10 said work was ongoing with nine potential suppliers on developing an antibody test which would show whether people have had the virus.

(PA Graphics)

Such a test would enable people to get back to work quickly and some experts say this type of testing is the quickest way out of the current lockdown.

Mr Johnson’s spokesman said: “We are working as quickly as we can on that and as soon as a test is approved then we will announce it publicly.”

He said the UK government had previously been offered tests that had not met the required levels of accuracy “and therefore would not have been safe to use”.

It was also suggested that immunity certificates to identify people who have had coronavirus are being considered by the government.

Mr Johnson’s spokesman said: “This is something which has been discussed in other countries.

“We have always said that we are watching closely what other countries are doing and we will always look to learn from ideas which could be helpful.”